For the effective functioning of a hydraulic machine, it is essential that the relative positional displacement amongst the various component parts, viz., body, flange and cover is controlled within reasonable limits. This factor helps to maintain reduced clearance between the gear tip circle diameter and the bore of the body, so that the hydraulic machine's volumetric efficiency can be kept optimum at various levels of oil pressure.
The desired performance is met by the hydraulic machine construction by employing positive close fit dowel arrangement between the flange and the body. Such a construction ensures that the relative movement amongst these two components is minimal.
Presently, the design of hydraulic machines is such that they are provided with dowels disposed on the body at the inlet side in case of two hollow dowels and at both inlet and outlet sides in case of four hollow dowels. These hollow dowels accommodate the mounting bolts of the hydraulic machine to pass through.
FIG. 1 of the drawings accompanying the specification depicts the profile of a pump body used in a conventional gear pump. Gear pumps using such profile and having two hollow dowels are, and can be, employed satisfactorily for applications requiring up to 3000 lbs./in2 (207 bar) oil pressure. The hollow dowels used in the body of a conventional gear pump is shown in FIG. 2 of the drawings accompanying the specification.
FIG. 3 of the drawings accompanying the specification shows the profile of a gear pump body used in a conventional gear pump where the application pressure required is high. Gear pumps using such profile and having four hollow dowels are, and can be, employed satisfactorily for applications requiring up to 4000 lbs./in2 (275 bar) oil pressure.
It is known from GB-A-2247923 to provide one or both ends of the housing with a non-circular inner rim which is received within a recess of matching non-circular shape defined by a flange projecting from a peripheral region of a respective end cover in a direction parallel to the axis of rotation of the meshing rotors. One or both open ends of the housing is thus supported by its end cover against outward deflection under the effect of fluid pressure in the chambers in a plane transverse to the axes of rotation of the meshing rotors.
GB-A-2247923 further discloses that the non-circular inner rim and matching non-circular recess are difficult to machine accurately and require complex CNC programming. Also, although this arrangement provides good alignment and support in a direction normal to the aforesaid plane (i.e. in the direction of the minor axis), no support is given in the direction of the major axis. Under the influence of internal pressure, the major sides of the housing deflect outwards to a small extent whilst the minor sides of the housing contract away from the mating edges of the peripheral flange on the end cover. The flange thus only limits body deflection in an outwards direction. Furthermore, there has to be an axial clearance between the peripheral flange and the end face of the housing in order to ensure that the end face of the inner rim seats against the base of the recess. The end cover is secured to the housing by bolts and this axial clearance results in a bolt load overhang which imposes a considerable bending load on the flange profile.
It is also known from GB 2408070A to provide a rotary positive displacement hydraulic machine in the form of a gear pump or motor comprising defining two mutually intersecting parallel working chambers having a low pressure inlet side and a high pressure outlet side, two meshing rotors mounted for rotation in the two chambers respectively, and two bearing supports at opposite ends of the chambers and each supporting bearings in which the two rotors are journalled for rotation, wherein at least one end of the housing is closed by a separate end cover and wherein the separate end cover and an adjacent end of the housing each has at least one elongated recess on each of the two major sides of the working chambers, the recesses in the end cover being alignable with respective recesses in the adjacent end of the housing and there being at least one keying element in each pair of aligned recesses so that the open end of the housing is supported against outward deflection by differential fluid pressure in the chambers in a direction transverse to a plane containing the axes of rotation of the meshing rotors.
There was a long-felt need in the art for an interlocking device for hydraulic machines, in particular, gear pumps operating at pressure in excess of 275 bar that prevents the undue relative displacement and the undesirable orientation of the gear pump body with respect to its flange and cover. A higher relative displacement between the structural component parts, of the gear pump will correspondingly lower the performance of the pump, particularly its volumetric efficiency, as discussed above. A crucial factor, and hence a matter of concern for gear pump designers, is the effectiveness of the doweling arrangement to prevent relative displacement of the pump body and the flange at the operating pressure.
Therefore, the strategy for improving the effectiveness of the interlocking arrangement is considered as a major step towards achieving high pump performance levels with increased volumetric efficiency.
With the above objective, the present invention is oriented towards optimizing the configuration of the dowel, i.e., its shape and size and also its disposition on the body of the hydraulic machine. This critical shape and size of the locating dowel and its optimal positioning have been arrived at in the present invention through in-depth estimation of the hydraulic forces occurring inside the pump body, which significantly behaves like a close knit pressure vessel, while being in high pressure operation.
In order to identify the optimum interlocking concept, pump interlocking arrangement using four bean-shaped dowels (as depicted in FIG. 4 of the accompanying drawings) has been evaluated for gear pumps operating at higher application pressure in the range of 330 bar, and compared for the relative strength and optimality with respect to the conventional hollow dowel arrangement.
The location of occurrence for the maximum stress and deflection position are different in the bean-shaped dowel arrangement according to the present invention as compared to the oval-shaped dowel arrangement invention according to the main invention, due to variation in the body profile and dowel profile and location. The optimality in deflection and stress for the body of a hydraulic machine while being used under extreme operating conditions makes it clear that the bean-shaped dowel arrangement is an improvement upon the oval-shaped dowel arrangement, as elucidated in further detail in the description hereinafter.